Images and letters are conventionally formed by printings on cover sheets of brochures and books and used for predetermined purposes. It is desired that the cover sheets of brochures and books are protected with a film according to their applications, e.g., protected from water and contamination, or for having gloss. Methods of protecting the cover sheets include overprint, vinyl coating, press coating, filming, etc. These methods make printed surfaces treated after printed. Among these methods, varnish applications are mostly used to form a protection (film) layer to protect printed surfaces with films.
Meanwhile, information frequently changes, and printers capable of producing variable information, e.g., partially changing the information increase. On-demand printings are used for this, and printings at higher speed are desired.
Electrophotographic and inkjet image forming apparatuses are used for on-demand printings, and the electrophotographic image forming apparatuses using a toner are mostly used to produce printings including images.
The electrophotographic image forming method reproduce an image color by transferring a powdery color material called a toner to a recording material such as papers. A fixer fixing a toner uses a roller, etc., formed of a material having good releasability. In order to further improve separability between the roller and a recording material after the toner is fixed, a large amount of oil is applied to the surface of the roller.
However, when a large amount of oil is applied to the surface of the roller, the recording material is contaminated with the oil. In addition, the fixer needs a space containing the oil and becomes complicated and large, resulting in cost increase.
Therefore, recently, electrophotographic image forming apparatuses have needed oilless mechanism without offset prevention mechanism with silicone oil for the purpose of simplifying the fixer and preventing the oil from influencing images such as oil contaminations and oil stripes. In addition, the oil is not applied to the fixing roller to improve fixability of a toner at from low to high temperatures. Instead, a wax is included in a toner.
Offset printings use some commercially-available varnishes to form protection layers on their printed surfaces. However, when the commercially-available varnishes are used in the electrophotographic image forming apparatuses, the wax included in a toner and the varnish do not match each other.
In order to solve this problem, Japanese published unexamined application No. 2007-277547 discloses a varnish composition and a preparation method thereof improving coatability on a toner layer with a water-based film former excluding ammonium and having a low static surface tension to oil-coated printed materials produced by electrophotographic oil fixing methods.
This prevents the varnish composition from being repelled by a fixing oil from the fixing roller applied all over a printed material due to its low static surface tension when applied thereto.
However, even when the varnish can be coated on a toner image formed of a wax-containing toner without being repelled on a printed material produced by electrophotographic image forming methods using a wax-containing toner, adherence between the varnish layer hardened after coated and the toner image is low, resulting in possible peeling of the varnish layer.
Japanese Patent No. 2522333 discloses electrophotographic image forming methods on metallic containers. Directly or through an electroconductive covering layer, a photoconductive titanium oxide photosensitive layer, a toner image layer and a finishing varnish layer are sequentially layered on a metallic container. However, high-frequency induction heating instead of a fixer including a fixing roller is used to heat metallic containers to fix a toner image thereon, and therefore there is no problem of adherence of a recording material to the fixing roller. A wax is used as a binder such that the toner adheres to the metallic container and is different from a wax preventing a recording material from adhering to the fixing roller.
Because of these reasons, a need exists for a wax-containing toner forming a toner image on which a varnish layer having a practical adhesion strength and glossiness for long periods can be formed.